With the ever-shrinking sizes of circuits and devices in very large scale integrated circuits, more and more defects on the wafer are associated with lower tolerances to manufacturing errors in specific points thereon. In order to analyze defects with respect to their specific localization and layout on the die, more and more CAD data is starting to be available in the manufacturing facilities. However, due to the low accuracy of defect localization reporting by the inspection tools (on the order of 1 micron) the usefulness of this information is limited to analysis of high resolution defect review images.
Inspection tools register an image of one die to an image of another die (perform die-to-die registration) in order to perform accurate comparison which is not degraded by stage inaccuracy. Registration includes measuring an offset between the two die images and shifting one die image relative to the other die image until the two die images coincide. The accuracy of registration is very important to the full extraction of the defect detection sensitivity of the inspection tool and registration accuracy much finer than the imaging pixel were reported.
There is a need to provide highly accurate registration methods and systems.